In article ,
(Snowbird) wrote:
I'm still trying to understand how a powered OFF radio with
the power OFF in the plane might be contributing to this
problem and hoping someone will explain this to me.

Does it help to think about how crystal radios work without any power at
all? Except for that of the transmitted signal.

Similarly, the energy for creating the interfering signal could be
coming from two or more transmitted signals that are mixing in the
front-end stage of an on-board radio receiver. Powered-off doesn't
matter; the energy is supplied by the transmitted signals and the mixing
action provided by one of the semiconductors in the first RF stage of
the receiver. Resulting interfering signal is then re-radiated back out
the same antenna the original signals are coming in on. You then hear
the interfering signal in another radio, such as a handheld.

Similarly, some corrision at an antenna terminal can also provide a
mixing action to a pair of strong signals that is then heard on one or
more radios. Or the aforementioned "rusty bolt syndrome" in that a
corroded bolt in a radio tower leg provides the mixing action for two
strong signals heard in your radios as you get close to it.

I would take the handheld and a car (or another airplane) and explore
the area where the interference occurs to eliminate the airplane from
the equation. Once you've convinced yourself it is or is not in the
airplane you have a direction to follow to find resolution. Until then,
you just don't know which way to look.

--
-Mark